Complex Magnetic Susceptibility Research Articles

Syntheses, structures and magnetic properties of four manganese(ii) and cobalt(ii) complexes

Hydrothermal reactions of Mn(II)/Co(II) salts and H4qptc in the presence of corresponding auxiliary N-donor ligands produced four novel complexes, {[Mn2(qptc)(4,4′-bibp)(H2O)4]·2H2O}n (1), [Mn2(qptc)(1,4-bib)(H2O)8]n (2), [Co2(qptc)(4,4′-bimbp)(H2O)2]n (3) and {[Co2(qptc)(1,3-dpp)(H2O)3]·H2O}n (4) (H4qptc = 1,1′:4′,1′′:4′′,1′′′-quaterphenyl-2,4,2′′′,4′′′-tetracarboxylic acid, 4,4′-bibp = 4,4′-bis(imidazolyl)biphenyl, 1,4-bib = 1,4-bis(1-imidazoly)benzene, 4,4′-bimbp = 4,4′-bis(imidazol-1-ylmethyl)biphenyl, 1,3-dpp = 1,3-di(4-pyridyl)propane). Single-crystal X-ray diffraction analysis showed that these complexes have different structures, including a 1D chain (2), a 2D layered structure (3), and a 3D network (1 and 4), depending on reaction conditions. Complex 1 is a 4,6-connected porous 3D framework with the point symbol (44·62)(44·610·8), which is composed of infinite 2D networks pillared by a 4,4′-bibp bridging ligand. 2 is a 1D zigzag chain, and the adjacent chains extend to a 3D supramolecular structure via non-covalent interactions involving contributions from carboxyl–water clusters. 3 is a 2D layer framework with an unprecedented topology, which are packed into a 3D supramolecular architecture by π⋯π and C–H⋯π interactions. 4 is a 4,6-connected 3D network with a Schläfli symbol of (3·4·54)(32·4·55·66·7). Furthermore, the magnetic susceptibility of complexes 1–4 have been investigated. 1 and 4 display weak antiferromagnetic behavior, 2 shows weak ferromagnetic interactions, and 3 exhibits different magnetic properties depending on temperature.

Field-dependent Brownian relaxation dynamics of a superparamagnetic clustered-particle suspension.

The distinguishable Brownian relaxation dynamics of a clustered-particle system of superparamagnetic iron oxide nanoparticle suspension compared to that of a dispersed-particle system has been experimentally investigated through characterization of the frequency and field strength dependences of complex magnetic susceptibility. We confirmed that the application of low sinusoidal magnetic field strength enables cluster rotation instead of individual particle rotations. Furthermore, we found that the cluster rotation was altered to individual particle rotations in higher field strength, resulting in a shorter Brownian relaxation time, which suggests a change in the hydrodynamic volume. This evolutional relaxation behavior was associated with a change in the fitting parameter which satisfies the empirical model of relaxation and further represents the significance of interparticle interactions in defining the nonlinearity of the magnetization response.

Geophysical signatures of disseminated iron minerals: A proxy for understanding subsurface biophysicochemical processes

Previous studies have linked biogeophysical signatures to the presence of iron minerals resulting from distinct biophysicochemical processes. Utilizing geophysical methods as a proxy of such biophysicochemical processes requires an understanding of the geophysical signature of the different iron minerals. Laboratory experiments were conducted to investigate the complex conductivity and magnetic susceptibility signatures of five iron minerals disseminated in saturated porous media under variable iron mineral content and grain size. Both pyrite and magnetite show high quadrature and inphase conductivities compared to hematite, goethite, and siderite, whereas magnetite was the highly magnetic mineral dominating the magnetic susceptibility measurements. The quadrature conductivity spectra of both pyrite and magnetite exhibit a well-defined characteristic relaxation peak below 10 kHz, not observed with the other iron minerals. The quadrature conductivity and magnetic susceptibility of individual and a mixture of iron minerals are dominated and linearly proportional to the mass fraction of the highly conductive (pyrite and magnetite) and magnetic (magnetite) iron minerals, respectively. The quadrature conductivity magnitude increased with decreasing grain size diameter of magnetite and pyrite with a progressive shift of the characteristic relaxation peak toward higher frequencies. The quadrature conductivity response of a mixture of different grain sizes of iron minerals is shown to be additive, whereas magnetic susceptibility measurements were insensitive to the variation in grain size diameters (1–0.075 mm). The integration of complex conductivity and magnetic susceptibility measurements can therefore provide a complimentary tool for the successful investigation of in situ biophysicochemical processes resulting in biotransformation or secondary iron mineral precipitation.

Structure and Magnetic Properties of a Trinuclear Nickel(II) Complex Constructed by bpca– Anions

AbstractThe trinuclear NiII cluster [Ni3(bpca)2(bpy)2(H2O)4](NO3)4·H2O (1) (bpca– = anion of bis(2‐pyridylcarbonyl)amine, bpy = 2, 2′‐bipyridine) was isolated. Single crystal X‐ray diffraction analysis showed that three crystallographically independent NiII ions are located in a six‐coordinate distorted octahedral environment, bridged by the organic spacer bpca–. The crystal lattice is stabilized by hydrogen bonds, which are linking the Ni3 cations and NO3– anions into a three‐dimensional framework. Variable‐temperature magnetic susceptibility for complex 1 in the range 2–300 K indicates the presence of weak antiferromagnetic interactions in the Ni3 unit with J = –0.67 cm–1.

Calibration of frequency‐domain electromagnetic devices used in near‐surface surveying

ABSTRACTFor the past forty years electromagnetic prospecting instruments have played a growing role in the mapping of soil EM properties in the very low‐frequency (VLF) range for a large variety of applica tions and they are now beginning to be applied in the medium‐frequency range. Measurement interpretations, however, necessitate expressing the results in terms of physical properties. This step allows not only comparisons and joint interpretation with data generated by different electromag netic induction (EMI) instruments but also with other types of field measurements e.g., vertical electrical sounding (VES) or electrical resistivity tomography (ERT) or laboratory tests on samples.The calibration process here proposed is based on comparisons between the instrument respons es and: (1) an exact 1D multi‐layer analytical modelling that takes the three EM properties into account, i.e., the electrical conductivity, the complex magnetic susceptibility and the complex die lectric permittivity when the instrument is elevated above a layered ground; (2) the response to purely conductive metallic spheres, which only depends on the diameter of the spheres. It is applied to two instrument prototypes: one in the VLF frequency range and the other in the medium‐frequency (MF) range.

A New Adamantane-like Tetranuclear Manganese(III) Complex Based on Flexible Schiff-base Ligand: Synthesis, Crystal Structure and Magnetic Property

A new tetranuclear Mn(III) complex <TEX>$[Mn^{III}{_4}(sae)_4({\mu}_3-O)({\mu}_{1,1}-N_3)(OH)(H_2O)_2]{\cdot}H_2O$</TEX> (1) (<TEX>$H_2sae$</TEX> = 2-salicylideneamino-1-ethanol) has been synthesized by the reaction of <TEX>$MnCl_2{\cdot}4H_2O$</TEX>, <TEX>$H_2sae$</TEX> and sodium azide in the mixed solvent of methanol, acetonitrile and water. The X-ray diffraction analysis shows that the four Mn(III) ions in complex 1 have a unique adamantine arrangement, whereas the coordination environment of each Mn(III) ions is different. Magnetic studies indicate that complex 1 manifests antiferromagnetic behaviors. The magnetic susceptibilities of complex 1 have been fitted by two magnetic models based on the suitable analysis of its magnetic structural topology.

Innovative Instrumentation to Measure Magnetic Susceptibility

A simplified instrumentation with nominal circuitry has been developed to measure in- and out-of-phase complex magnetic susceptibility of bulk magnetic samples. A unique shape of the absolute coil is implemented to improve the magnetic field homogeneity inside the coil. Complex susceptibility of nano-composite is measured by an innovative phase detection circuit. In this paper, we also discuss in detail the principle, design, and the performance of the instrumentation. This susceptometer is also suitable for liquid samples, viz., ferro-fluids, blood samples, etc.

Synthesis, structure and magnetic investigations of polycarboxylato-copper(II) complexes

Polynuclear Cu(II) complexes bridged by multicarboxylate compounds (1,4,5,8-naphthalene-tetracarboxylic acid, H4nptc; 2,5-pyridinedicarboxylic acid, 2,5-H2pydc; 1,3,5-benzenetricarboxylic acid, 1,3,5-H3btc; tris(acetato)amine) have been synthesized and characterized by IR and UV–Vis spectroscopic techniques. These compounds include [Cu4(pmedien)4(μ4-nptc)(H2O)4](ClO4)4·2H2O (1), [Cu2(pmedien)2(μ2-2,5-pydc)(H2O)](ClO4)2·H2O (2), [Cu3(DPA)3(1,3,5-btc)(ClO4)3]·H2O (3), [Cu3(DPA)3(HN(CH2COO)3)(H2O)3](ClO4)4·3H2O (4), and [Cu3(pmedien)3(HN(CH2COO)3)(H2O)3](ClO4)4·2H2O (5) where pmedien=N,N,N′,N″,N″-pentamethyldiethylenetriamine and DPA=di(2-pyridymethyl)amine. X-ray single crystal crystallography reveal the tetra- and di-nulear bridging nature of the fully deprotonated acids H4nptc and 2,5-H2pydc in complexes 1 and 2, respectively. Magnetic susceptibilities of complexes 1 and 2 which were measured at variable temperatures showed very weak antiferromagnetic coupling.

Hydrogen-Bond Directed 1D and 3D Cyanide-Bridged Heterometallic Complexes: Synthesis, Crystal Structures and Magnetic Properties

By employing K2[Pd(CN)4] as building block, [Mn(L)(H2O)2]ClO4 or Mn(Phen)2Cl2 (L = N,N-ethylene-bis(3-methoxysalicylideneiminate; Phen = 1,10-phenanthroline) as assembling segment, a trinuclear cyanide-bridged heterometallic Pd(II)-Mn(III) complex {[Mn(L)(H2O)]2[Pd(CN)4]}2·4H2O (1) and a ion-pair complex [Mn(Phen)2(H2O)2][Pd(CN)4] (2) have been synthesized and characterized by elemental analysis, IR spectroscopy and X-ray structure determination. Single X-ray diffraction analysis reveals the cyanide-bridged trinuclear complex 1 is self-complementary through coordinated aqua ligands from one complex and the free O4 compartments from the neighboring complex, therefore giving 1D single chain supramolecular structure. For complex 2, it is constructed into interesting 3D network depending on the intermolecular O···H–N hydrogen bond interactions. Investigation over magnetic susceptibility of complex 1 reveals the overall weak antiferromagnetic coupling between the adjacent Mn(III) ions. With [Pd(CN)4]2− as cyanide building block and bicompartimental schiff-base manganese(III) compound or Mn(II)-phenanthroline compound as assembling segment, one heterobimetallic cyanide-bridged trinuclear clusters and one heterobimetallic ion-pair complex have been synthesized and characterized by elemental analysis, IR spectroscopy and X-ray structure determination, in which the trinuclear complex 1 is self-assembled into one-dimensional chain structure by the intermolecular O–H⋯O hydrogen bond interactions, while the ion-pair complex 2 is linked into interesting three-dimensional network supramolecular structure by the intermolecular O–H⋯N hydrogen bond interactions. The trinuclear structure (top) and 1D single chain structure (bottom) constructed by intermolecular hydrogen bond interactions for complex 1. The crystal structure of ion-pair complex 2 (top) and its three-dimensional supramolecular structure constructed by intermolecular O-H⋯N hydrogen bond interactions (a axis (top), b axis (middle), c axis (bottom)). The magnetic property of complex 1.

Nonequilibrium dynamics of a spin-3/2 Blume-Capel model with quenched random crystal field

The relaxation and complex magnetic susceptibility treatments of a spin-3/2 Blume-Capel model with quenched random crystal field on a two-dimensional square lattice are investigated by a method combining the statistical equilibrium theory and the thermodynamics of linear irreversible processes. Generalized force and flux are defined in irreversible thermodynamics limit. The kinetic equation for the magnetization is obtained by using linear response theory. Temperature and also crystal field dependencies of the relaxation time are obtained in the vicinity of phase transition points. We found that the relaxation time exhibits divergent treatment near the order–disorder phase transition point as well as near the isolated critical point whereas it displays cusp behavior near the first-order phase transition point. In addition, much effort has been devoted to investigation of complex magnetic susceptibility response of the system to changing applied field frequencies and it is observed that the considered disordered magnetic system exhibits unusual and interesting behavior. Furthermore, dynamical mean field critical exponents for the relaxation time and complex magnetic susceptibility are calculated in order to formulate the critical behavior of the system. Finally, a comparison of our observations with those of recently published studies is represented and it is shown that there exists a qualitatively good agreement.

Electrical excitation and detection of magnetic dynamics with impedance matching

Motivated by the prospects of increased measurement bandwidth, improved signal to noise ratio, and access to the full complex magnetic susceptibility we develop a technique to extract microwave voltages from our high resistance (∼10kΩ) (Ga,Mn)As microbars. We drive magnetization precession with microwave frequency current, using a mechanism that relies on the spin orbit interaction. A capacitively coupled λ/2 microstrip resonator is employed as an impedance matching network, enabling us to measure the microwave voltage generated during magnetisation precession.

Sub-micron mapping of GHz magnetic susceptibility using scanning transmission x-ray microscopy

We report submicron imaging (∼0.75 μm resolution) of complex magnetic susceptibility in a micron-size ferromagnetic heterostructure using time-resolved scanning transmission x-ray microscopy. The real and imaginary parts of the susceptibility are extracted from the phase and amplitude of the small-angle (&amp;lt;20°) rotational response of the local magnetization under microwave excitation. Frequency-dependent response patterns were observed in an incompletely saturated bilayer element. The technique is extensible to higher frequencies (to ∼10 GHz), better spatial resolution, and layer-specific measurement.

Size effect of Fe nanoparticles on the high-frequency dynamics of highly dense self-organized assemblies

Molded Fe nanoparticle (NP) assemblies 4 mm × 8 mm × 0.3 mmt in size were fabricated by a uniaxial press from Fe NPs 3 nm to 22 nm in diameter, and their high-frequency dynamics and static properties were investigated. The freezing temperature of the magnetic moment of the assemblies increased from 25 K to over 400 K with an increasing Fe NP diameter, and for particles larger than 8.1 nm, the Fe NP assemblies showed ferromagnetic behavior even at room temperature. For particles smaller than 8.1 nm, on the contrary, the assemblies showed superparamagnetism at room temperature. From the complex magnetic susceptibility spectra of the assemblies normalized by the volume of the Fe NPs, χ′Fe, and χ″Fe, the minimum ferromagnetic resonance frequency, fr (106 MHz), and maximum χ′Fe at 1 MHz (123) were obtained at 8.1 nm. The fr of the Fe NP assembly increased because of an enhanced magnetostatic interaction field between NPs larger than 8.1 nm. For NPs smaller than 8.1 nm, in the superparamagnetic phase, the thermal magnetic field increasingly dominated the effective magnetic field with a decreasing NP diameter. This indicates the existence of a critical diameter for the thermal fluctuation of the moment, which competes with the magnetostatic interactions between the Fe nanoparticles.

Brownian relaxation of magnetic nanoparticles in fluid: the effect of the solvent

The magnetic contribution of the solvent on the RT ac magnetic susceptibility behaviour of Fe3O4 magnetic nanoparticles in solution at different concentrations, is presented and discussed. The room temperature complex susceptibility of the solvent water was studied as a function of several parameters, namely different ac fields, superimposed dc fields, different pHs and temperature: in any case a transition from a diamagnetic behaviour to a paramagnetic one at a characteristic frequency (~4,500 Hz) was observed. These results were compared with the data obtained for other common organic solvents. A dependence of the complex magnetic susceptibility from the polarity of the solvent was observed. The results were discussed in terms of a paramagnetic contribution of polarization to the whole measured susceptibility proportional to the applied frequency. For the real and imaginary susceptibility of water at room temperature, empirical polynomial equations as a function of the frequency were obtained. On the basis of these fits, the observed complex susceptibilities of the different nanoparticles solutions were corrected from the solvent contribution and the results are presented.

An experimental study of the dynamic properties of nanoparticle colloids with identical magnetization but different particle size

Measurements of the frequency dependent complex magnetic susceptibility, χ(ω)=χ′(ω)−iχ″(ω), have been used to determine the dynamic properties of three specially prepared 400G (0.04T) magnetic fluids. The samples, denoted by sample 1, sample 2 and sample 3, consisted of magnetite particles of mean diameter 6.4nm, 7.5nm and 9nm respectively and were identical in terms of carrier liquid, surfactant and particle material.From polarized ferromagnetic measurements, the anisotropy field, HA, the Landau–Lifshitz damping parameter, α, and the precessional decay time, τ0 of the particles were determined. The results show that the HA value for sample 3 was almost twice that of sample 1 and 2, thus confirming that the smaller the particle size, the lower the value of HA. The damping parameter, α, was found to be 0.174 (for sample 1), 0.18 (for sample 2) and 0.16 (for sample 3). The values determined for the precessional decay time, τ0 were 1.197×10−9s, 1.157×10−9s and 0.789×10−9s, for samples 1, 2 and 3 respectively.

Analysis of heating effects (magnetic hyperthermia) in FeCrSiBCuNb amorphous and nanocrystalline wires

The induction heating effects in amorphous and nanocrystalline wires, Fe73.5-xCrxSi13.5Cu1B9Nb3 (x = 3, 7, and 10), are analyzed in this work. In these alloys, the Curie temperature of the amorphous phase, TC, can be tailored through the Cr content of the alloy or the volume crystalline fraction after nanocrystallization. Four samples were selected; amorphous with x = 0 and 10 and nanocrystalline x = 7 with different crystalline fractions. The Curie temperature of the residual amorphous phase, TCa, was experimentally determined by the temperature dependence of the self-inductance of the samples. The analysis of the frequency dependence of the complex magnetic susceptibility enabled the estimation of the magnetic power losses in the samples. The heating effects on the wires were analyzed under the application of an ac magnetic field employing a home-made hyperthermia set-up. A single piece of a wire was immersed in a water bath (initial temperature from 291 K to 325 K) and subjected to the ac magnetic field. The specific absorption rate (SAR) was estimated through the initial slope of the temperature increase as a function of time. Maximum SAR values were obtained in the amorphous sample (x = 3) with the highest TC and enhanced magnetic power losses. In the nanocrystalline samples (x = 7), the detected heating effects above TCa are interpreted as a consequence of the magnetization process of the ferromagnetic grains. However, in spite of the low SAR displayed by the amorphous wire with TC ≈ 300 K (x = 10), interesting self-regulated characteristics are observed in this sample.

Synthesis, Structure, and Magnetic Property of a New Manganese Coordination Polymer with 2-(pyridin-2-yl)-1H-imidazole-4,5-dicarboxylic Acid

A new one-dimensional Mn(II) complex, {[Mn2(HL)2(H2O)4]· 2DMF} n (H3L = 2-(pyridin-2-yl)-1H-imidazole-4,5-dicarboxylic acid), has been prepared and characterized by elemental analyses, IR, TG analysis and single crystal X-ray diffraction. The single-crystal XRD study revealed that the complex crystallizes in a space group P-1 and has a 1D Zigzag chain. In addition, the variable temperature magnetic susceptibility of complex 1 was measured and weak antiferromagnetic exchange interactions between the neighboring Mn(II) ions was found.

Microwave absorption by magnetic nanoparticles in the organism

An estimate of the rate of absorption of the electromagnetic microwaves by magnetic nanoparticles in organisms is presented. The absorption takes place due to the energy dissipation at the ferromagnetic resonance. Based on the known solution of the Landau-Lifshitz equation, the imaginary part of the complex magnetic susceptibility is evaluated that gives the absorption rate. It is shown that even in the conditions of thermal isolation of the particles, their temperature growth would be insignificant at absorption of the emission with the energy flux density of the order of 1 mW/cm2, and the given mechanism is unrelated to the observable effects of low-intensity microwaves.

Modeling of isochronal complex magnetic susceptibility of polymer–magnetic nanocomposites using fractional calculus

AbstractIn this work, we report on the application of fractional calculus to the modeling of the isochronal behavior of complex magnetic susceptibility obtained from polymer–magnetic nanocomposites composed of cobalt‐ferrite nanoparticles embedded into a chitosan matrix. From the isochronal measurements of real and imaginary parts of the complex magnetic susceptibility and temperature‐dependent static measurements, performed at different applied dc‐fields, it was observed that the spins' response is mainly leaded by three contributions, which are attributed to the intrinsic magnetic anisotropy of the particles, the surface‐to‐core spins exchange within particles and to the dipole‐dipole interactions among particles. Accounting these contributions, the proposed magnetic model was capable to describe, in very precise way, the experimental behavior of both, real and imaginary, parts of the complex magnetic susceptibility, at temperatures below to that related to the transition of the polymer–magnetic nanocomposite into the superparamagnetic regime. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Intra-well relaxation process in magnetic fluids subjected to strong polarising fields

We report on the frequency and field dependent complex magnetic susceptibility measurements of a kerosene-based magnetic fluid with iron oxide nanoparticles, stabilized with oleic acid, in the frequency range 0.1–6GHz and over the polarising field range of 0–168.4kA/m.By increasing polarising field, H, a subsidiary loss-peak clearly occurs in the vicinity of the ferromagnetic resonance peak, from which it remains distinct even in strong polarising fields of 168.4kA/m. This is in contrast to other reported cases in which the intra-well relaxation process is manifested only as a shoulder of the resonance peak, which vanishes in polarising fields larger than that of 100kA/m.The results of the XRD analysis connected to the anisotropy field results confirm that the investigated sample contains particles of magnetite and of the tetragonal phase of maghemite.Taking into account the characteristics of our sample, the theoretical analysis revealed that the intra-well relaxation process of the small particles of the tetragonal phase of maghemite may be responsible for the subsidiary loss peak of the investigated magnetic fluid.